# Interacting virtual particles?

## Main Question or Discussion Point

static fields - quantum picture

I am trying to understand quantum field theory & QED but i am having problems, because i don't find specific answer:

What is the real quantum difference between electric and magnetic field?

Maybe in spin of virtual photons (1, 0, -1)? But then what is polarization of light?! Or is the key here electric & magnetic momentum of a particle?!? Help

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vanesch
Staff Emeritus
Gold Member
Marjan said:
I am trying to understand quantum field theory & QED but i am having problems, because i don't find specific answer:
What is the real quantum difference between electric and magnetic field?
Could you elaborate on what specifically you're asking ?
The EM "field" in QFT is usually taken to be the 4-potential A_mu. If you understand well how A_mu is related to the electric and magnetic fields (a prerequisite before hoping to understand the quantum version of electromagnetism) then I don't understand your question, because the relationship is the same.
If you don't understand that relationship, then you should first learn more about classical EM. Does the field tensor F_mu,nu tells you something ?

cheers,
Patrick.

Chronos
Gold Member
Try to work out the moments and their potentials.

Ok, like vanesch said - one step back!

Magnetic momentum of single fundamental (lets take electron) particle is pm = g*e*(1/2 hbar)/(2*m), where g is approx. 2.

Electric dipole(!) momentum of electron and positron is pe = e*l, where l is distance between them. And pe is oriented opposite of E field.
So, is the electric momentum of a single particle pe = e*x, where x is "size" of fundamental particle?!

Am i right? If so, I just proved that fundamentally we can't talk about just one of the fields (like magnetic or electric), because every fundamental particle have mass and charge, so it have also el. AND magn. momentum.
And then i guess: B = M / pm and E = M / pe or something like that?!

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What is the real quantum difference between electric and magnetic field?
Acutally magnetic fields are really electric fields that arise due to length contraction in general relativity. There is a really good example that describes this involving the magnetic field created by a wire with current running through it. I'll try to find it on-line.

Holy s*it, you are right. I think I just bumped into Quantum Physics / General Relativity problem. One or the other, but not both together!

Two points:

(1) Magnetic field is born just for observer who is in relative motion according to electric charge. So magnetic field is just a side effect of relativity. Even more: Magnetic field's origin is in (general) relativity!

(2) Is spin=0 of photon possible state? Yes, but only in sistem of other photons or gravitons. No way for fermions.

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Do you see that it's all fine, if we examine problem through relativity OR through quantum physics?! But can't both!

Entropy, did you have something like that in mind: [URL [Broken] ]Field Relativity.[/URL]

I draw that picture, it is little funny, but try to understand what i am trying to say

It is up to observer if he will measure field or energy (-> also mass)!

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Do I have a point or am I just going crazy? :surprise: